Coordinates in ggplot2 in R
The coordinate system of a plot refers to the space on which the data is plotted. The coordinate system of a plot, together with the x and y position scale, determines the location of geoms.
Below are the available coordinate options:
coord_cartesian
: This is the default coordinate system (x horizontal from left to right, y vertical from bottom to top)coord_flip
: Flipped cartesian coordinate system (x vertical from bottom to top, y horizontal from left to right)coord_trans
: Used to to transform the coordinate system. We, i.e., substitute traditional axes with logarithmic axes and then present the values and statisticscoord_equal
: Ensures the units are equally scaled on the x-axis and on the y-axiscoord_polar
: Polar coordinate system; the x (or y) scale is mapped to the angle (theta)coord_map
: Various map projections
Most popular graphs such as line and bar charts are drawn using Cartesian coordinates.
coord_cartesian
When we plot a chart, Cartesian Coordinates is the default coordinate system. For example, the following chart plots Duration of Credit on x-axis and Credit Amount on y-axis. The points are colors by the factor Loan.Quality.
1g <- ggplot(df,aes(x=Duration.of.Credit..in.months.,y=Credit.amount,color=Loan.Quality))
2g+geom_point()+geom_smooth()+coord_cartesian()
3

coord_flip
By specifying coord_flip, it will still use the cartesian system, but flip the two axis.
1g <- ggplot(df,aes(x=Duration.of.Credit..in.months.,y=Credit.amount,color=Loan.Quality))
2g+geom_point()+geom_smooth()+coord_flip()
3

Zooming In
We can use the coordinates layer to zoom in to a plot by setting limits. The various options are below:
1coord_cartesian(xlim = NULL, ylim = NULL, expand = TRUE)
2
xlim, ylim
: Limits for the x and y axes.expand
: If TRUE, the default, adds a small expansion factor to the limits to ensure that data and axes don't overlap. If FALSE, limits are taken exactly from the data or xlim/ylim
Let's say we want to zoom in our plot to show the points where the Duration of credit is between 40 and 60. This can be done as follows:
1g <- ggplot(df,aes(x=Duration.of.Credit..in.months.,y=Credit.amount,color=Loan.Quality))
2g+geom_point()+geom_smooth()+coord_cartesian(c(40,60))
3

Aspect Ratio
We can set the aspect ratio of a plot with coord_fixed()
or coord_equal()
. Both use aspect = 1
(1:1) as a default. For example, consider the following plot which plots Duration of Credit on x-axis and Age on y-axis.
1g <- ggplot(df,aes(x=Duration.of.Credit..in.months.,y=Age.in.years,color=Loan.Quality))
2g+geom_point()+geom_smooth()
3

We can add the coordinate coord_equal() to make the aspect ratio 1:1.
1g <- ggplot(df,aes(x=Duration.of.Credit..in.months.,y=Age.in.years,color=Loan.Quality))
2g+geom_point()+geom_smooth()+coord_equal()
3
